1. Field of the Invention
The present invention relates to a semiconductor device manufacturing method and, more particularly, to a method for reforming a surface to reduce surface dependency in film formation by a thermal chemical vapor deposition method (thermal CVD method) using a reaction gas (referred to as an “O3/TEOS reaction gas” hereinafter) containing TEOS (tetraethylorthosilicate) and an ozone-containing gas including ozone (O3) in Oxygen (O2) and, in a semiconductor device manufacturing method employing this reforming method. “Surface dependency” means that formation of the CVD film grown on the film-forming surface is affected in growth rate, etc., by the chemical properties of the surface on which it is formed.
2. Description of the Prior Art
In recent years, with the progress of super high density and multi-layered wiring in semiconductor devices, the development of technology for forming an insulating film demands superiority in surface planarity, recess filling, step coverage, and suppression of permeation of moisture and impurities. The film forming technology developed to satisfy these demands includes a method of forming the film by CVD using a O3/TEOS reaction gas. In this case, an excellent film can be obtained if the O3 concentration is set higher.
The influence of such surface dependency does not appear with a low O3 concentration, but is evident under conditions of high O3 concentration.
In the following description, the O3/TEOS reaction gas having a high O3 concentration is called a “high O3/TEOS reaction gas”, and a Silicon dioxide film formed by the CVD method using this reaction gas is called “high O3/TEOS SiO2 film”. Also, the O3/TEOS reaction gas having a low O3 concentration is called “low O3/TEOS reaction gas”, and a Silicon dioxide film formed by the CVD method using this reaction gas is called a “low O3/TEOS SiO2 film”. In general, the Silicon dioxide film formed by the CVD method using the O3/TEOS reaction gas containing various O3 concentrations is called simply an “O3/TEOS SiO2 film”.
FIG. 16 is a sectional view showing the state in which the film has grown abnormally due to the influence of surface dependency.
In the prior art, in order to eliminate surface dependency, the methods shown in FIGS. 17A to 17D are employed. These methods are:
(i) irradiating a plasma onto the film-forming surface (FIG. 17A),
(ii) covering the film deposition surface with a plasma CVD SiO2 film (FIG. 17B),
(iii) forming a low O3/TEOS CVD SiO2 film as an underlying layer prior to film formation of the high O3/TEOS CVD SiO2 film (FIG. 17C), and
(iv) forming a thin low O3/TEOS CVD SiO2 film, irradiating the surface of the film with a plasma, and forming the high O3/TEOS CVD SiO2 film on the low O3TEOS CVD SiO2 film (FIG. 17D). In the above methods (iii) and (iv), double layers consisting of the low O3/TEOS CVD SiO2 film and the high O3/TEOS CVD SiO2 film are employed.
However, the conventional methods have the following respective problems.
(i) With the method of irradiating a plasma onto the film deposition surface, conditions suppressing the surface dependency are varied. Therefore, since the conditions can neither be standardized nor shared for all film deposition surfaces, the conditions must be optimized for each film deposition surface.
In addition, separate plasma CVD equipment must be provided to generate the plasma.
(ii) In the method covering the film deposition surface with a plasma CVD SiO2 film, some process conditions provide a film that is compatible with a high O3/TEOS CVD SiO2 film that exhibits good film properties. However, since the plasma CVD SiO2 film has poor step coverage, the plasma CVD SiO2 film is not suitable for fine patterns. Also, plasma CVD equipment must be separately provided.
(iii) Covering the film deposition surface with the low O3/TEOS CVD SiO2 film, since the low O3/TEOS CVD SiO2 film has very good affinity to the high O3/TEOS CVD SiO2 film, eliminates the surface dependency. However, the low O3/TEOS CVD SiO2 film shows isotropic growth characteristics, and a film thickness of at least 100 nm is needed to enable use of the film as an underlying film that eliminates surface dependency.
Therefore, such low O3/TEOS CVD SiO2 film is unsuitable for fine patterns.
Though the method of eliminating the surface dependency by using the low O3/TEOS CVD SiO2 film that was formed under low pressure was examined, this film was essentially the same as the low O3/TEOS CVD SiO2 film, and therefore was unsuitable for fine patterning for the same reason.
(iv) Covering the film deposition surface with a low O3/TEOS CVD SiO2 film and then irradiating the film with a plasma makes the method complicated.
Thus, the conventional methods are generally not suitable for filling a narrow and deep recess, while recent demand for high density in semiconductor devices requires a method for forming an interlayer or cover insulating film that has superior film properties, and especially a method that can fill a narrow and deep recess.